470 Notices of Memoirs — Dr.- T. Sterry Hunt — 



of successive strata of limestone and detrital matters. The argil- 

 laceous portions of these, it is conceived, may have taken part in the 

 reactions with thermal waters. We have thus, in the opinion of the 

 author, a reasonable mode of accounting for the origin of the various 

 rocks of the crystalline formations, and a consistent and complete 

 Neptunean theory which does not involve the aid of metasomatosis. 

 It has, since it was proposed eighteen years ago, met with the 

 approval of many whose studies have made them the fittest judges 

 of its reasonableness. Among those who have either formally given 

 their adhesion to it, or have enunciated similar views, may be 

 mentioned the names of Delesse, Eenard, Giimbel, Credner, Alphonse, 

 Favre, and Gastaldi. 



The chemical activities concerned in the produotion of the various 

 silicates have doubtless suffered gradual change and diminution 

 through the successive ages of Eozoic time, from which have re- 

 sulted mineralogical and lithological differences in the crystalline 

 terranes. Each of these includes quartzites and limestones, in 

 which latter certain silicates, such as serpentine, hornblende, and 

 micas, are occasionally found. It is in those aluminiferous rocks, 

 which are without lime or magnesia, that are seen the essential and 

 characteristic difierences dependent, as long ago pointed out by the 

 author, upon a decrease in the proportion of alkalies. As we pass 

 from the older to the younger of the Eozoic terranes, the felspar, 

 orthoclase, and albite become partially or wholly replaced by 

 silicates like muscovite, damourite and paragonite, and finally by 

 andalusite, fibrolite, cyanite, and pyrophyllite. The author alluded 

 briefly to the changes by which the ancient aqueous deposits were 

 transferred into crystalline stratified rocks by what Giimbel has 

 designated as diagenesis, as distinguished from their supposed origin 

 by epigenesis or metasomatic change. The question of the relation 

 of the indigenous rocks to the endogenous and exotic masses in- 

 cluded in them was noticed, the author alluding to the hypothesis 

 which he has elsewhere maintained that the source of all exotic or 

 eruptive rocks is to be found in the displacement or extravasation 

 of ancient deposits of Neptunean origin. 



Coming to the second division of his subject, the author asserted 

 that the study of the crystalline rocks of North America shows the 

 existence of several distinct groups or terranes. The Laurentian, which 

 is the most ancient, includes in its lower part a mass of unknown 

 thickness of granitoid gneiss, often hornblendic (Ottowa gneiss), 

 succeeded, perhaps unconformably, by what has been called the Gren- 

 ville series, consisting of similar gneisses and hornblendic rocks, with 

 intercalated quartzites and iron ores. These two divisions make up 

 together the Lower Laurentian of Logan, of which the thickness in 

 Canada may greatly exceed 20,000 feet. The Norian, which is the 

 Upper Laurentian, or Labradorian of Logan, rests unconformably 

 upon the Laurentian, and is remarkable for a great development of 

 rocks composed chiefly of Labradorite, or related plagioclase fel- 

 spars, which have been called Labradorite-rock, or Norite. The 

 interstratified gneisses, quartzites, and limestones of the Norian are 



